Overview of Technology
Kureha microspheres (MS) are a precision additive that are used to lower density, reduce cost, and provide acoustic and thermal insulation. When heated, microspheres expand to a target diameter and maintain that diameter after cooling.
As the temperature reaches the thermal start (Ts) of the selected grade, the hydrocarbon pressure inside the polymer shell increases while the shell itself softens. Fully expanded, the microsphere increases 3-5X its original diameter with a 80-120X increase in volume.
Kureha microspheres are flexible in application and processing. They are compatible in both binder and fibrous materials; and can be compressed during molding and rebound to the intended shape when the pressure is reduced. Kureha offers grades that activate (Ts) from 100C up to 210C. Customers get a controlled and predictable expansion without the discoloration and outgassing issues of chemical foaming agents; or breakage that is common with hollow glass spheres.
Kureha employs a unique manufacturing process compared to other polymer microsphere suppliers. The outcome is tighter control over particle distribution with superior dispersion (resists agglomerations) characteristics.
Under equal weight, Kureha Microspheres render better volumetric filling and are 30%-85% lighter than alternative mineral additives. All of our grades maintain their durability with the added benefit of helping to reduce material cost and weight. Through consistent and accurate particle size distribution, each of our grades offer low thermal conductivity to provide extremely efficient thermal barrier properties. See a comparison of particle destiny, expansion ratios and particle sizes for each grade of Kureha Microspheres in the charts below.
Comparison to Other Microsphere Additives
Despite the technical definition, glass, polymer, ceramic, fly ash (cenosphere) and metallic spheres are often marketed as «microspheres». Each has its unique application, manufacturing method and synthetic base. Because of this, they are not interchangeable within an application.
However, they do sometimes overlap in purpose. For instance, most of the above mentioned products can be used as a volumizer, or to reduce cost, weight, insulate or improve surface finishes. Expandable polymer microspheres are unique because they have all of these attributes. They also share performance features with chemical based additives like CBA’s and CFA’s
Typically these are chemically resistant with a very low CTE. Glass spheres are high density and are commonly used as a volumizer for resin displacement or to inhibit agglomerations. They are used in marine fillers and putties to reduce shrinkage and reduce thermal conductivity in wet pipe insulation. They can also be coated and used for flow visualization or by a compounder as an alternative to solvent for lowering material viscosity. Stainless steel microspheres on the other hand often function as ball bearings or conductive spacers in bonding applications.
Fly Ash Cenospheres are composed of silica and alumina and are a byproduct of coal burning power plants. They exhibit high compressive strength (3000 psi) and have low moisture absorption properties. Primary uses include low viscosity fillers for cement, tiles and foam composites.
Ceramic Microspheres are inert, hard and can withstand extreme processing and application temperatures. They have good insulative properties and compressive strength. Typical applications include industrial and decorative paints or as a grinding media.
Chemical Foaming and Blowing Agents
The flexibility of expandable polymer microspheres makes it an excellent tool to reduce density/weight. Because of this they are often used in conjunction or to replace CBA’s (Chemical Blowing Agents) or CFA’s (Chemical Foaming Agents). That includes AZOD (Azodicarbonamide), OBSH (Oxydibenzenesulfonyl Hydrazide) and Sodium Bicarbonate among others. These agents are either endothermic or exothermic and decompose in the base material. Generally speaking grades differ by gas pressure and the amount of gas liberated per gram.
The issue with both chemical and foaming agents comes down to control. Controlling color, density, durometer and surface finish can be challenging when you’re trying to aggressively reduce density. Additional complications that come with working with working with these agents include molding times and mold corrosion; and in the case of organic foaming agents, the odor from outgassing
Polymer microspheres offer a more efficient and predictable solution for creating uniform pour structures in materials.